The synthesis of histones during lytic infection of BSC-1 (African Green Monkey kidney) cells with Simian Virus 40 (SV40) has been investigated. The synthesis of all five classes of histones was stimulated, and all classes appeared to be stimulated to the same extent. The increase in rate of histone synthesis in response to SV40 infection was detectable several hours before SV40 DNA synthesis was measurable, and the rate of histone synthesis decreased at a time when SV40 DNA synthesis was occurring at a maximal or relatively high rate. In addition, the changes in rates of histone synthesis did not correlate well with the rates of host DNA synthesis during infection. Thus it appears that DNA synthesis and histone synthesis may not be strictly coupled in SV40 infected cells.